The present invention relates to an amphibious vehicle.
The phrase “sandwich power take off” or “sandwich PTO” as used herein refers to a power take off which is positioned between, and separates, the engine and a speed change transmission in a power train. Such a power take off is driven by an engine main output shaft, typically a crankshaft; and drives a transmission input shaft.
In an amphibious vehicle, particularly a planing amphibious vehicle, it is advantageous to use a power train in which an engine and transmission are positioned towards the rear of the vehicle. The weight of the power train is therefore positioned towards the back of the vehicle, which is necessary for good vehicle performance when the vehicle is in marine mode. Furthermore, the position of the power train maximises the space available towards the front of the vehicle for the passenger compartment.
A power train is disclosed for use in an amphibious military personnel carrier in U.S. Pat. No. 5,752,862 (Mohler). The disclosed power train uses a rear mounted engine and a combined transmission and differential mounted at the front of the vehicle. Although Mohler uses the drive shafts from the differential to drive caterpillar tracks, such drive shafts could also be used to provide drive to the front road wheels of a civilian amphibious vehicle. However, the power train arrangement disclosed in Mohler has several disadvantages for application to such a civilian vehicle. First, the location of the transmission at the front of the vehicle may reduce passenger and/or luggage space. Secondly, the arrangement requires a propeller shaft running through the passenger area. This shaft, which carries full engine power and rotates at engine speed, takes up valuable passenger space and will generate noise. Third, front wheel drive is not an optimal solution for a rear engined vehicle, as traction will not be as good as if the engine weight is placed over the driven wheels. This can give problems for example in take-off on slippery surfaces, and unusual on-road handling characteristics.
Other power train arrangements for use in an amphibious vehicle are known from U.S. Pat. No. 5,590,617 (Aquastrada) and U.S. Pat. No. 3,765,368 (Asbeck). In these power trains an engine and transmission are connected end-to-end in conventional automotive rear wheel drive fashion, but with the overall arrangement reversed to drive the front wheels. As can be seen particularly clearly from Aquastrada, this forces the passenger seating area towards the front of the vehicle, followed by a long rear deck area, which cannot be used for passenger or luggage space.
U.S. Pat. No. 2,350,037 (Hofheins et al) describes an amphibious vehicle in which an engine drives an output shaft by way of a transmission unit. A marine propulsion propeller is driven through a drive shaft which has an operative connection with a take-off shaft projecting from the transmission unit. A clutch for controlling driving engagement to the take-off shaft is also provided. However, the power take-off in Hofheins is not positioned between the engine and transmission and is not a sandwich power take-off, and cannot therefore transmit as much power. Hofheins also has the disadvantage that due to the relative positioning of the components, the shaft to the propeller has to slope downwards when the propeller is in use; but must be withdrawn into the vehicle when not in use. The drawbacks of this layout include the complication of an additional clutch unit, and the fact that the universal joints run at a constant angle when the propeller is in use, leading to vibration and shortened service lives. Where a shaft passing through a hull moves up and down, flexible seals must be provided, which will need maintenance; and water seepage into the hull will inevitably occur.